In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Specifically, ultraviolet radiation such as g-line and i-line radiation has conventionally been used, but nowadays KrF excimer laser (248 nm) is mainly mass-produced and also ArF excimer laser (193 nm) has begun to be introduced in mass production.
In the resist for such a shorter wavelength light source, high resolution which enables reproduction of a pattern of minute dimensions, and higher sensitivity to such a shorter wavelength light source are required. One example of a resist material that satisfies these conditions is a chemically amplified resist composition including a base resin and an acid generator (PAG) which generates an acid upon exposure. Chemically amplified resist compositions include positive compositions in which alkali solubility increases, and negative compositions in which alkali solubility decreases.
Examples of PAG that has been used in chemically amplified resist compositions are onium salts, and a multitude of onium salts have conventionally been proposed. In patent document 1 shown below, PAG comprising a triphenylsulfonium onium salt is described. Of these acid generators, an onium salt acid generator containing fluorinated alkylsulfonic acid ions as an anion (acid), such as triphenylsulfonium nonafluorobutane sulfonate (TPS-PFBS), is used most commonly.
[Patent document 1]
Japanese Unexamined Patent Application, First Publication No. 2003-167347